1. Field of the Invention
The present invention relates to a lamp driving system controlled by electrical isolation, and more particularly to a lamp driving system that uses an electrical isolator to control the signal isolation.
2. Description of Related Art
According to the IEC1000-3-2 international specification, a power supply having an input power over 75W needs to have a power factor correction (PFC) function, and thus a front-end power stage of a power supply generally includes a power factor correction controller. The power factor correction controller is a prior art that performs a power factor correction to an AC power while reducing the harmonic current in the power supply and producing an output of a constant voltage approximately equal to 400V.
Referring to FIG. 1 for a schematic circuit block diagram of a lamp driving system in accordance with a prior art, the lamp driving system 1 includes a power factor correction controller 10, an isolating DC/DC converter 12, a switching circuit 14, a PWM controller 16, a boost transformer 18, a loading resonant network 19, a voltage regulator 13 and a system controller 15.
A front-end power stage of the prior art lamp driving system 1 includes a power factor correction controller 10 and an isolating DC/DC converter 12. The power factor correction controller 10 receives an alternate current power AC and produces an output of a constant high voltage HV. The isolating DC/DC converter 12 converts a constant high voltage isolation into the output of a repeated voltage VCC for the back-end power stage of a prior art lamp driving system 1. The back-end power stage includes a switching circuit 14, a PWM controller 16, a boost transformer 18 and a loading resonant network 19. The prior art lamp driving system 1 uses a voltage regulator 13 to convert AC power into outputs of voltage in various different specifications, and the output voltage is provided for a system controller 15, a PWM controller 16, or other circuits.
When the prior art lamp driving system 1 is lit, the system controller 15 will output a start control signal ST to notice the PWM controller 16 to start lighting up the lamp, and the PWM controller 16 will produce a control signal SPWM to control the switch of the switching circuit 14. The switching circuit 14 switches the repeated voltage VCC to output a high-frequency switching power to the boost transformer 18, and the boost transformer 18 will boost the high-frequency switching power to a high-voltage switching power output for the loading resonant network 19. The PWM controller 16 will obtain a feedback signal SFB from the loading resonant network 19, and adjust the output of the control signal SPWM according to the feedback signal SFB to maintain the stability of the lamp driving system 1.
In a traditional lamp driving system 1, the front-end power stage requires a power factor correction controller 10 to improve the power factor, lower the harmonic current and produce a constant voltage, but the constant high voltage produced by the power factor correction controller 10 will affect the operations of the back-end PWM controller 16, the system controller 15 or other controllers. Therefore, the traditional lamp driving system 1 needs to use an isolating DC/DC converter 12 in the front-end power stage for the electrical isolation and voltage step-down, so as to assure the normal operation of the circuit in the back-end power stage.
In general, the isolating DC/DC converter 12 includes components such as a transformer, a controller, a switching circuit and a feedback network, and thus the isolating DC/DC converter 12 of a traditional lamp driving system 1 has a much higher price than other components, and the isolating DC/DC converter 12 occupies quite a large volume in the overall component layout of the lamp driving system 1.
With the consideration of the overall price and component layout of the lamp driving system, it is an important subject for manufacturers to waive the use of an isolating DC/DC converter 12 in a lamp driving system that requires a power factor correction controller to improve the power factor by providing a back-end power stage electrically isolated lamp driving system.